1. Field of the Invention
The present invention relates to high temperature, solid oxide electrolyte electrochemical cells and cell configurations and the electronic connection of such cells and configurations.
2. Description of the Prior Art
High temperature, solid oxide electrolyte fuel cell configurations, and fuel cell generators, are well known in the art, and are taught by Isenberg, in U.S. Pat. Nos. 4,395,468 and 4,490,444. These fuel cell configurations comprise a plurality of individual, series and parallel electronically connected, axially elongated, generally tubular cells. Each cell is electronically connected in series to an adjacent cell in a column, through narrow cell connections extending the full axial length of each cell. These connections contact the air electrode of one cell and the fuel electrode of an adjacent cell, through a conductive ceramic interconnection and a fiber metal felt strip. Other than one embodiment showing segmentation of the cells in U.S. Pat. No. 4,490,444, all support, electrolyte, electrode, interconnection and fiber metal strip components extended the entire length of the cell.
The felt strip current collector, made, for example of nickel fibers, bonded at contact points, extended axially between the cells. In the preferred embodiment, air was flowed inside the cells and gaseous fuel outside. The nickel felt used in the preferred embodiment was about 70% to 97% porous and was generally made according to the teachings of Brown et al., in U.S. Pat. No. 3,895,960, and Pollack, in U.S. Pat. Nos. 3,702,019 and 3,835,514, all involving the use of solid nickel fibers, and metallurgical, diffusion bonding at fiber contact points, at about 900.degree. C. to 1,200.degree. C.
Self-supporting, low circumferential voltage gradient, solid oxide electrolyte fuel cells were developed by Reichner in U.S. Ser. No. 034,245, now U.S. Pat. No. 4,767,681 filed on Apr. 6, 1987, and assigned to the assignee of this invention. There, an electronically conducting central portion was added to the axial air electrode and utilized to strengthen it, eliminating a need for a separate support. This central portion allowed ease of electron travel to axial, conductive, ceramic interconnects, which covered only a small middle section of the air electrode top surface, and which supported fiber metal felts which were disposed parallel to the fuel cell length and gas flow. Elongated configurations, providing a flattened fuel cell with a plurality interior gas feed chambers were also taught. Here again, all support, electrolyte, electrode interconnection and fiber metal strip components extended unbroken, the entire axial length of the cell.
White, in U.S. Pat. Nos. 3,402,230, and 3,460,991, taught a self-supporting, one piece, tubular, high temperature, solid electrolyte fuel cell tube. There, an elongated, tubular, gas tight series connected cell stack was taught, with solid electrolyte generally disposed between air electrodes and fuel electrodes. The cell tube was formed as a continuous tube, rather than assembled as a series of individual cells. Gaps between the cells were filled with an overlap of top air electrode, overrunning the underlying solid electrolyte, to physically and electrically contact the bottom electrode forming an electrode-to-electrode connection on the tubular structure. Calcia stabilized electrolyte was taught, along with a variety of cathode and anode materials. Electronic connections, shown as conductive wires between individual fuel cell stack tubes were made in series, directly from the end inner electrode of one cell struck tube to the end outer electrode of a parallel, adjacent cell stack tube.
Larger diameter, self-supporting, stacked, solid oxide electrolyte fuel cells were developed by Isenberg in U.S. Pat. No. 4,728,584, and. There, a fuel cell was made up of a plurality of individual cell elements with an annular, electronically conductive interconnection member between each stacked, discrete element. Each cell element on adjacent fuel cells in series was staggered from the other. Conductive assembly connectors contacted interconnection ring members of an adjacent fuel cell. These conductive assembly connectors, shown as thin conductive wires, were disposed at a 90.degree. angle to the former, axially oriented metal fiber felts of the Isenberg structures, taught in U.S. Pat. Nos. 4,395,468 and 4,490,444. Thus the electrical connections between adjacent, stacked fuel cells was transverse rather than parallel to fuel cell axial length and gas flow. These conductive assembly connectors only connected two cells together, i.e., the fuel electrode of one cell to the interconnection ring of an adjacent cell, which interconnection ring contacted the air electrode of the adjacent cell. This type of construction, however, provides for many joints and complicates fabrication of the fuel cell itself and assembly into cell stacks.
None of these configurations provides for a simple geometry and connection pattern between adjacent fuel cells that allows stronger, larger cells, with greater power per unit, and eliminates circumferential voltage drop in the air electrode and non-uniformity in electrolyte current density.
3. Object of the Invention
It is the object of this invention to provide new types of solid oxide electrolyte electrochemical cell combination and array configurations, utilizing continuous air electrode supported fuel cells, having contacting, circumferential, electronic connections and supports, and to greatly simplify assembly procedures for stacks of series and parallel connected cells.